Liquid crystal display (LCD) has many advantages, such as, light weight, energy saving, no radiation, and accordingly has gradually replaced traditional cathode ray tube (CRT) display. LCDs are widely used in high-definition digital televisions, desktop computers, personal digital assistants (PDA), notebook computers, mobile phones, digital cameras, and other electronic devices. An LCD typically includes a backlight module and an LCD panel disposed above the backlight module.
Wide viewing angle is the mainstream development of an LCD. Presently, portable electronic devices such as notebook computers, personal digital assistants, tablet PCs, mobile phones are adopted with wide viewing angle technology, so that users can see the display images on the LCD without distortion when viewed from different viewing angles. However, when using the portable electronic device in public places, the wide viewing angle design of conventional LCD cannot effectively protect the privacy of the user, and the images displayed on the LCD can be easily viewed by a bystander in a squint direction. Therefore, in addition to the needs for a wide viewing angle, LCDs capable of being adjusted to a narrow viewing angle are thus developed in order to protect modern people's needs of privacy in public places.
Currently, there are mainly two ways to switch between a wide viewing angle and a narrow viewing angle in an LCD. One way is to use a louver shielding film to cover the screen so as to reduce the angle of view in the need for protecting privacy. However, this way needs preparation of an additional louver covering film, causing great inconvenience to the user. One louver covering film can only achieve a fixed viewing angle. Once a louver covering film is attached to the screen, then the viewing angle of the screen is fixed and cannot change according to requirement of the user. The other way is to provide a dual light source backlight system in the LCD to adjust the angle of view. The dual light source backlight system consists of two layers of laminated light guide plates in combination with an anti-prism lens, the top light guide plate (LGP-T) combined with the anti-prism lens is used to change the direction of lights and restrict the lights in a relatively narrow range to obtain a narrow viewing angle in the LCD, while the bottom light guide plate (LGP-B) combined with the function of the anti-prism lens is used to obtain a wide viewing angle in the LCD. However, the dual light source backlight system will cause the thickness and the cost of the LCD to increase remarkably, which is not in line with the development trend of light weight, compactness and slimness of the LCD.